Small electric motor



March 18, 1952 E. L. scHELLENs 2,589,293

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March 18, 1952 E. L. scHELLl-:Ns 2,589,293

SMALL ELECTRIC MOTOR Filed DBC. 14, 1949 2 SHEETS--SHEET 2 CM b 9]/ ATTORNEYS.

Patented Mar. 18, 1952 f UNITED STATES PATENT OFFICE SMALL ELECTRIC MIOTOR Eugene L. Schellens, Essex, Conn., assigner to R. W. Cramer Company, Incorporated, Centerbrook, Conn., a corporation of Connecticut Application December 14, 1949, Serial No. 132,812

9 Claims.

- l This invention relates to small electric motors, such as synchronous motors, whether of. the A. C. inductor or yother type. Suchinotors conventionally have certain basic elements, such as a multipoled, coil-energized, neld structure or stator, and cooperative therewith a multipoled rotor carried upon the motor shaft or sleeve; with usually a reducing gear train driven from what for convenience is herein termed the front or rotor end of the shaft. Such motors are of great advantage and have come into very large practical use, as for clocks, relays and various other light driving purposes. The'nearest prior small electric motor of the type mentioned known to this applicant is that 'disclosed in U. S. Patent No'. 2,492,197 granted December 27, 194:9,v upon the invention ofrapplicant, the application for which prior case was copending with this present case, which may be considered a parti-al continuation of the prior case, which in turn may be referred to for certain details not herein illustrated.

l A general object of the present invention is to improve lthe'general structure and framing,- and other stationary and component features of vmotors ofA the Vkind-referred to. Certain other p0rtions of thev herein disclosed motor, including the 4rotor and its mode of cooperation with the-stator, may bey substantiallyconventional. Another object is tov isolate and seal offfrom each other, by nieans of anon-ferrous cross wall or partition, in an improved and effective manner, the motor front space or compartment which contains the rotor and other parts, running in oil, and the annular rearl space or compartment wherein is located the energizing coil of the sta'- tor, thus shielding the coil from injurious access of oil thereto'.

4In said prior case the stationary general or freineelem'ents, including the iron stator inembers and the non-ferrous partition wall, were assembled under control of means for securing proper alinement, and thereupon were treated with molten solder,v preferably applied dry at'the intended joints and then subjected to induction heating'for melting and sealing purposes, and to interconnect the parts. This prior soldering systern of connectionr was extensively used, and proved to be generally satisfactory; but there were certain substantial drawbacks, including the need of heat, tending to interfere with the exactitude and permanence of the interconnections, as well as progressive deterioration of the assembling and holding xures and devices, due to the use of solder. Itis anV additional` object of the present invention to cbviate the defects thus outlined, namely, by the use of a system of dry or wholly mechanical means of and operations. for interlocking the assembled, centered and: alined fixed or frame parts of the motor. A 1

Further objects and advantages of the invention will .be made clear in the hereinafter iollowv ing description of an illustrative embodiment thereof. To the attainment of the re'cltedobjects and advantages the invention consists'ln the novel small electric motor and the novellen-I tures of combination, construction, arrangement and method and details herein illustrated :or described. if

The invention consists, in one specific aspect.' of the assembled motor elements, especiallyA the fixed elements, herein illustrated and described generally as follows. 'The stator as a whole has. successive iron portionsl providing the magnetic circuit, including the shouldered central core,vor member, and the rear and peripheral walls exa tending outwardly and frontwardly from the core rear end, and with an interior fixed ilangelwall or ring extending outwardly and frontwardly from the core front end. Said iron portions dene the annular compartment to receive the sta-r tor coil. The front terminal of said peripheral wall is formed, and may be considered, as a pole-1 carrying xed outer eld ring, -while the'ilang'e Wall as a whole, or its body, may be considered as an inner field ring. These two rings are adje#V cently arranged' and shaped to provide outer and inner series respectively of stator poles. The :ntor comprises also an interior non-magnetic par; tition or disk wall of annular form located adjacentiy frontward of the coil compartment but adjacently rearward oi said flange wall or inner ring. The partition inner rim is permanently joined to both the core member and the flange wall or inner ring by a liquid-tight first joint, while its outer or peripheral rim is joined to the inner side of the peripheral wall or outer ring by a liquid-tight second joint. 'Ihe motor so described is characterized in that the partition inner edge isengaged and seated upon the core shoulder or step in a position between and engag-v ing both such shoulder or seattand the inner margin of the ange wall or inner ring. The motor is characterized also in that the first of said joints consists of a staked lip extending from the front end of the core and tightly swaged over and-held under high pressure upon vthe ilange wall inner margin, whereby such ange wall man gin is held in squeezing pressure against the inner rim' of the partition, which in turn bears against.

the core shoulder, thereby permanently joining and locking tightly the core, the fiange wall or Y ring and the interposed partition. The motor is ,tional supplement the gear case rear wall has a rear flange or bent end annularly engaging a groove in the front end of the outer eld rinir and there staked by an annular metal lip swaged from the eld ring front face to overlie the rear wall flange and unify the gear case with the outer field ring and other permanent frame parts. The stator core and field rings to be liquid'tight should be machined; and the partition also should be accurately preformed at both rims.

`In the accompanying drawings, Fig. 1 is a central sectional View of a small motor embodying the-invention hereof, shown in a posture with its main shaft or spindle placed' horizontally, the parts thus being shown as seen from above. The front view appearance and the arrangement and shapes of the poles, as one example, may be ascertained by referring to the first figure of the prior case. 1 1

The main permanent or frame elements of the 'present motor are preferably assembled and interconnected in a special progressive order. As an illustration these main xed elements comprise the central core member of the stator, the outer poled field ring, and the inner poled or field ring, these parts being composed of iron; and also the non-'magnetic partition wall which isolates the stator coil compartment from the rotor compart ment; and supplementally, when desired, the gear case at the front, or rather the anged rear back wall thereof; all of these elements being herein made vrigidly unitary with each other; although Fig. 1 for clearness shows the several joints withoutthe final locking or swaging, shown in detail inithe following figures.

Fig. 2, on an enlarged scale, is a diagrammatic sectional view showing the principles of producing the mainsub-assembly, in this case of the core, the inner lield ring and the partition inner rim, the result constituting the partialj construction of the stator, with two joints provided in one step.` .L Fig. 3 is similar to Fig. 2, but showing the assembling carried further by staking the partition outer rim to the outer field ring, thus by this step combining four stator members, and attaining the object of isolation from each other of the coil and rotor compartments.`

Fignl shows the supplemental or final assembling step of staking the gearbox rear wall to the front end of the Youter field ring, obviating the disadvantages of using solder thereat. Fig. 4A is a detail View of part of Fig. 4 showing a minor desirable feature.

i' It will be appreciated that the described order of fassembly and interconnection of the main-fixed elements is only the preferable method; and that the nal rigid structure so produced corresponds with that shown in Fig. 1, but disclosing the means closing the joints not fullyu shown in Fig. 1.

To disclose more specifically the principles and method of producing the composite unitary rigid framing of the invention three gures are provided, corresponding with Figs. 2, 3 and 4, showing suitable equipment and illustrating in principle the steps for performing the successive interconnecting operations. Thus Fig. 5 shows diagrammatically the mechanically interconnecting steps for the stator portions shown in Fig. 2, involving a staking, spreading or swaging action to unify tightly the core, inner field ring and partition; a preferred kind of fixture or anvil piece being indicated, and a cooperating swaging or staking tool. Similarly, Fig. 6 shows a preferred means for interconnecting theouter eld ring to the subassembly of Figs. 2 and 5 in the manner shown in Fig. 3, thereby producing the subassembly of four fixed members. The assembly appears inverted in Fig. 6 as the staking is best done that way.

Finally, Fig. 7 shows a preferred means, fixture and staking tool, adapted for interconnecting with the partial assembly of Figs. 3 and 6, a gearbox or its rear wall by the staking thereof to the front end of the outer pole ring, completing the structural operations and framing steps.

Referring to the structural details, the coil 8, for energizing the stator is accommodated within the annular compartment 9. The stator itself, composed of soft iron members or portions II to I8, may be of different designs adapted to provide the conventional path of magnetic ilux, with which the movable element or rotor I9 cooper ates. The stator magnetic members are in end'- wise alinement, at some places unitary,l at other places in abutting contact, with convenentdivision lines between members. The central core I I demarks the inner boundary of the coil compartment and is shown as a generally cylindrical 'iron member formed with an axial bore IIA used. for

mounting the rotor axle or shaft.

At the rear end of the core is the enclosing rear wall I2, being a separate piece from the core and held in magnetic contact therewith as by an end screw I2A passing through a central aperture :of the wall and threaded into the bore of the core. The rear wall extends outwardlyfiom the'cor'e, i. e. laterally of the axis, to a peripheral pointer corner beyond which the stator extends frontwardly, in the form of a peripheral wall I3.

At its front end the peripheral Wall is provide or formed with a terminal piece or enlargement I4, which may be considered as the outer eld ring or pole ring of the stator, this carrying an outer series of stator poles I5. In the drawing the peripheral wall I3 is indicated as integral with .the rear wall I2, in which case the peripheral wall is separated as shown by a line of division from the fixed outer stator terminal piece or iiel'dring I4. This arrangement permits the combined walls I2 and I3, extending outwardly and frontwardly, to be attached by a sliding fit and bodily removed, being in the form of a cup, surrounding and completing the closure of the coil compartment, While permitting the opening of the compartment for insertion and removal of the coil. On theother hand,` if the rear and `peripheral walls I2 and-.I3 have a division line between them, asin said prior patent, the peripheral wall matr be formed integrally with the outer eld ring of the stator, and only the rear wall removed for access..A .As shown, the peripheral Wall I 3 when in place, if separate from the eld ring, seats in theoute recess or shoulder I4A of the latter.

The other branch of the stator structure and circuit, commencing at the front endl ofthe axial core I I, is shown as follows. In contact with and extending laterally vfrom the front endof the icore is an interior flange wall I1, this constituting-a field or pole ring separate from the core andextending first outwardly and then shaped `into a front extension, the front part at least orwhich is formed into a series of inner stator? poles- I8, having a fixedv position adjacent to thev outer series I5.

The: outer and inner stator pole seriesA I- and I-ifor-m` the conventional doublev series cooperating with the rotor I 9, which'hasV a series of poles YMlv and which turns about an axis coincident' with the center line of the stator core II. vThe rotor is preferablyv of the conventional disklike shape,

having a scalloped or indented. rim forming the poles, and these`v p'oles being permanently magnetized alternately or in other mannerto cooperate with the stator" poles. The'- rotor, by means' of its hub 2 I, is secured fast upon rotary sleeve 22, which may be considered the hollow shaft of the rotor. The sleeve in turn is arranged to rotate either with or upon the interior' shaft or axle 23, which extends through the sleeve and' therebeyond rearwardly' into the front end of the borel IIA of the stator core II. If the central member 23 be a fixed axle or' stud its tight engagement in the bore holds it as a steady rod or post. The shaft is shown as having the middle portion of its length reduced somewhat in diameter, leaving front and rear heads 24, with. the front head contacted A bya confined bearing ball 25.

' The enlarged front endv of the rotor Ashaft or sleeve 22 represents or carries a first gear 26, turned directly by the rotor. The rotor and the parts on which it is directly mounted are accommodated within the rotor compartment 27, being an annular space within the front terminals of the stator parts; while the gearing, which may f desired kind may be interposed between the first gear 28 and the output shaft 30 projecting from the front wall 3| of the gearbox or case.

The gear case 29 may be of any suitable construction, `its front closing wall 3I being preferablyy permanently united with a circumferential W-a-ll 32 which is oval and has, ask an inwardextension, a'rear wall 33, which is.v annular. The inner' margin of the rear wall is formed withl fi'- rea'rwardly bent curvedv extension or lowflange 34. entered within a circumferential receiving groove IAD preformed'. in. the". front rendl of the outer field ring I4. When so assembled the' ring. and low wall extension are` in positionv forl staking"l To ensure secure; interconnection the low flange nea-r' its extreme edge isA formed with a slight crimp or shallow4 gutter 35 which the staking lip Z- canover-lie: to lock this joint.

The non-magnetic partition` 40' is composed for exampleof brass, and4 is of annular disklilce form; and it isllocatedfrontward of the coil 'compa'.rt-` merit S but to the rear" of the flange wall or` inner eldring Il. The' partition: has an inner rim 4I tobe interconnected with the core I IY and inner -eld ring Il, and at itsoute'i-i' rim it is formed to be staked to thek outer ring I4, with a= curvedly bent extension 42 constituting a foot to be interconnected with thev ring I4.

-Asa collateral device'u the following is shown in Fig. l. A short stud 45, projected into the rotor vcompartment 2l, isl mounted fixedly with itsrear'end driven into'A registering round holes inthe' ring I1 and partition 40. On this stud turns freely a pinion 46', and this is in mesh with a central 'gear' 41 mounted fast upon the rotor shaft or sleeve, so that the pinion rotates and stops with the sh'afti The onset' idlerV pinion" 45 meshing with central gear 4l may function as a one-way device on the principles involving the gear 4I and gear 42 of prior Patent No. 2,436,231 of February 17, 1948.

Without at first referring to the assembling steps, the final relative positions of the fixed stator members or sections II, I4, Il and 40 will be described in detail. As stated, in Figi. lthe' final interconnecting ofthe members is not shown, all members however being in their proper relative positions, requiring only the staking or spreading' steps by which certain lips, .designated X, Y and Z, are swaged over, as from the central core for one of the joints and from the outer field ring for the other or' remaining joints.

The radial widthof the partition 40 is somewhat greater than the radial spacing between the core I I and the outer ring I4. This permits the core to' be formed with a shoulder or step IB, whichv is annular as are the other elements outside of the core' and the inner, rim 4I of the partition bears against the shoulder IIB, whereat it may have a snug or close fit upon the reduced end of the core. Beyond the partition rim the core is formed with a cutaway recess t 3C adapted to accommodate, with a similar close nt. the innerv margin of the inner field ring Il. The described shoulder and thel wider recess, as shown, are of such dimension that the ring margin bears directly against the partition rim when assembled. The front surface of the inner ring as thus assembled against the partition front face, may be substantially flush with the front end ol the core, as shown. The shoulder IIB is de fined in depth by the metal of the core radially inward of the partition position, and it will vbe note-l that this metal extends frontwardly short heV front face ofy the partition, so that when the ring margin is pressed rearwardly the pressure is taken solely by the partition rim which in turn is backed by the core metal forming the shoulder IIB. In other words a thin annularl space is provided inwards of the rim 4I and which reaches rearwards of the front face of the rim, seen in Figs. l and 5, so that the staking pressure upon the ring is received wholly on the rimv andv not at all .on the second shoulder of the core.

By these arrangements the partition and the inner ring take definite assembled positions on the core. These partsV moreover are under la substantial pressure, the partition inner rim being under squeezing pressureV between the core shoulder IIB and the inner ring margin. Now, when a portion or' lip of the Inet-al of the front end of the core is' staked, and bent over outwardly and rearwardly against the front face of the ring margin, this effects the tight joint between the three stator members, the core, the inner ring and the partition. The staking or swaging action thus referred to may in some cases bev effected without the preformation of a groove I tD to assist theheavy work of deforming the metal of the core memb'eriand overturning 'it to reach, bear against, and lock the ring and partition members as a part of the tight joint between these members. By this plan more core metal is provided for staking. y

The interconnection between the outer field ring I4 and the outer rim or bent foot portion of the partition is described as follows. At its inner side' the outer ring is formed with a shoulder MB, provided by a cutaway recess receiving the partition foot 42 and presenting an abutting surface for the extreme edge of the bent rim. The parts shown in Fig. 1 occupy this position, the curved corner of the bent rim of the partition standing adjacent to the inner surface of the ring; while the rear surface of the ring is substantially ush with the body of the partition. Atits rear face the ring is formed with a groove I 4C, and between this groove and the inner surface remains the metal constituting the lip Y which, when swaged, effects the interconnection at this joint. This groove 14C is preferablypreformed, and when the staking or spreading tool is applied to the groove and operated this causes the lip Y to be deformed and swaged toward the curved` corner of the partition and preferably spread varound that corner into overlapping relation to the outer rim of the partition, thus in-` terlocking the ring and the partition clear around the outer rim of the latter. The shoulder I4B takes the thrust. The description thus far completes'rwhat is necessary to provide the desired liquid-tightrpartition separating the coil compartment from the rotor and gearcase compartments of the motor.

At the front end of the outer eld ring I4 is shown'the means for effecting the desirable permarient interconnection of gearcase 29 with the stator-.'xed parts. The rearwardly bent or curved" end 34 of thegearcase rear wall 33 is shown engaged in a special recess I4D preformed in the front end surface of the ring. Inl order to provide ring metal thatl maybe swaged outwardly against and partly over the curved wall extension 34 a second groove ME is preferably preformed in the front surface of the ring, fairly close'to the recess I4D, but leaving enough metal to form the staking or swaging lip Z, which is thepart vforcibly bent over and against the low projecting edge 3d of the wall 33. To ensure rigid locking of the gearcase unit to the stator unit'or its fixed members, the low wall-flange 34 may be preformed o1' struck with an annular indentation or crimp ,35, producing a shallow def pression or gutter, as best seen in Fig. 4A, adapte ed to' receive part of the staked metal of the lip Z, as seen in Fig. 2. j

The'several assembling steps,"each followed by a staking or interconnecting step may be varied in their details and in their order of performance. As' one' example the 'stator core I I is rst staked,

seated' upon the shoulder I4A thereof, where it vmay be removably secured.

The steps thus described on the diagrams of Figs. 2, 3 and 4 may be performed by themeans indicated conventionally in Figs. 5, 6 and '7 respectively. Thus, Fig. 5 shows the core Il, inner ring I1 and partition 4l! loosely assembled upright, and engaged upona special fixture or support F serving also as a staking anvil. An implement or staking tool T may be fitted and power-operated, asa punch, to descend, with a pressure or blows, this having an annular blade or staking wedge t. which enters the groove I ID, when such a groove is preformed, or forms its own groove, the wedge being straight at its inner face but inclined outwards at the other side, vthereby to force the lip X of core metal to spread outwardly, over and upon the face of the ring, in the manner seen in Fig. 2. The base fixture or anvil F supports properly the three members and takes the thrust of the staking operation.

Likewise, Fig,V 6 shows the combined members II, I'I and 4t assembled loosely with the outer eld ring It and supported upon a special base fixture F2. The parts are inverted, relative to Fig. 5, so that the tool or punch T2 can act downwardly against the ring, its wedging bladel t2 striking into the staking groove |4C; the wedge being inclined in a manner to deform and spread inwardly the lip- Y, with the result shown in Fig. 3.

Similarly, referring to Fig. '7, this has a base fixture or jig F3 and cooperating with it a staking tool Ta with wedging or spreading edge t3. The combined members II, Il, 4!) and I4 are assembled-With the gearcase wall 33, upon the fixture; and in operation the acting edge t3 enters the preformed groove ME o f the already fixed outer ring I4, thus forcibly spreading the lip Z of ring metal, so as to spread and overlie the low yflange 34 andso unify the wall 33 with the ring, with as illustrated vin Fig. 2, both to the inner field ring I1 and to the inner rim of the partition 4l! assembled therewith, said rim being squeezed or pinched upon the core shoulder I IB by pressure upon the ring, the parts becoming united anc"v joined by the formation, from the metal of the core', of the staking lip X. Following this doublestaking rst operation, the outer. rim d2 of the partition,l now attached to the core and inner ring, as in Fig. 3 shown, is staked to the outer ring i4, pressure being applied to force the rim to itsseat I 4B and the parts becoming joined `permanently by the swaging'of the lip Y. Therethe result of la joint such as shown in Figsr-f and 4A.

There`has thus been described a small electric motor, shown as a synchronous motor, embodying the principles and attaining the advantages of the present invention; but since many matters of combination, operation, method, construction, arrangement and detail may be variously modified without departing from such principles it is not intended to limit the invention to such matters except to the extent set forth in the appended claims. v

What is claimed is:

`1. A small electric motor of the type described having at the front and rear respectively a pfolcd rotorand a cooperating poled stator, said stator having successive iron portions providing its magnetic circuit and defining an annular coil compartment, including a shouldered central core, and outer and inner polerings shaped to provide outer and inner series of stator poles; andsaid motor comprising a-non-ferrous metal partition of annular form located adjacently frontward of such coil compartment, with its inner rim connected by a rst joint to both said core and said inner pole ring, and its outer rim connected by a second joint to said outervpole ring; and characterized in that the partition has its inner V`rim extended into` engagement between theA core shoulder and the inner margin of the inner ring, and in that such first joint comprises astaked lip extending from the front part of the core and tightly swaged over and against such inner margin of the inner ring, whereby the inner ring is held by its inner margin in squeezing pressure against the inner rim of the partition with thrust against the core shoulder, thereby permanently interlocking and joining tightly the core, the inner ring and the interposed partition; and characterized further in that said second joint comprises a staked lip extending from the rear part of the outer pole ring and tightly swaged over and against the partition outer rim, with thrust against the outer pole ring shoulder.

`2. A small motor as in claim 1 and wherein the flange wall constitutes the inner one of two pole rings, the outer one of which at its front end is formed with a recess enclosing the bent edge of the rear wall of a gearcase; and the outer pole ring having a staked lip adjacent to said recess, swaged over against the gearcase bent edge in a manner to interlock the outer ring and gearcase thereby to unify rigidly the motor stator fixed portions and the gearcase.

3. A small electric motor of the type set forth having at the front and rear respectively a poled rotor and a cooperating poled stator, said stator having successive fixed iron portions providing its magnetic circuit, including a central core, and walls extending outwardly and frontwardly from the core rear end, providing an outer pole ring, and a flange wall providing an inner pole ring extending outwardly and frontwardly from the core front end, said iron portions dening an annular coil compartment; and said motor characterized in comprising also a non-ferrous bridging and spacing partition of annular form located frontward of such coil compartment but adjacently rearward of said inner pole ring, with its inner rim connected by a iirst joint to both said core and said inner ring, and its outer rim connected by a second joint to said outer ring, thereby spacing apart and positioning and centralizing the two rings; the inner one of said two joints comprising a staked lip extending from the core portion into a holding position securing the inner rim of said partition to such xed iron portion.

4. In an electric motor of the type set forth wherein the stator includes an axial core, and concentric therewith an inner pole ring and an outer pole ring, all composed of iron, the core having a reduced end part providing a circum ferential shoulder and recess; and in combination therewith a non-ferrous partitioning and centralizing annular disk bridging from ring to ring;

the disk being arranged with its inner rim seated and clamped upon said core shoulder, and the inner pole ring having its inner margin seated and clamped upon said disk inner rim with the exposed side thereof substantially flush with the adjacent reduced end part of the core; and the core at such reduced end having an integral lip swaged out from the core metal and extending outwardly and tightly against the inner pole ring inner margin with the parts under high compression; whereby the disk inner rim is held tightly under high squeezing pressure, the thrust of which is taken by the core shoulder, and whereby the core, the inner pole ring and the disk are permanently joined; and means permanently.

joining the outer rim of the bridging disk to the outer ring, with the latter centered in correct functional relation to the inner pole ring.

5. An electric motor as in claim 4 and wherein the means joining the outer disk rim to the outer eld ring consists of a staking lip extending from the ring and overlying the disk rim under pressure.

6. A motor as in claim 5 and wherein the outer ring is formed with a shoulder to take the pressure thrust, and the disk outer rim is formed with a bent foot seated on said shoulder; and wherein the staking lip overlies the curved bend of the disk rim.

7. A motor as in claim 4 and wherein is a gearbox permanently connected to the stator fixed parts, the gearbox having an annular rear wall with a bent low-ange extension for interconnection with the stator outer iield ring; and said outer ring having an end recess accommodating said flange extension, and having an integral lip staked over and upon said extension.

8. For a motor of the type set forth, a stator enclosing an annular coil compartment and comprising the following series of iron members, (l) a Wall member partially bounding the coil compartment, and, as permanent xed members, (2) a central core 'having near one end an annular shoulder, said bounding wall member being attached to and removable from the other end of the core member for access to the coil compartment, (3) an outer iield ring, and (4) an inner iield ring, the inner margin of which is swaged to the first mentioned core-end beyond said shoulder by mechanical deformation of the core metal; together with an annular partitioning member or disk which is non-ferrous and is held under liquid-tight pressure at its inner rim between the core shoulder and the inner eld ringv margin, and whose outer rim is secured rigidly and liquid-tightly to the outer field ring; the outer iield ring being rigidly supported by said partitioning disk member and thereby indirectly from the central core member.

9. In a small electric motor of the type described, a poled stator having magnetically alined iron portions dening an annular coil compartment, including a shouldered central core, and outer and inner pole rings shaped to provide an outer series surrounding an inner series of stator poles; and said stator comprising a .non-ferrous metal partition of annular form located adjacently frontward of such coil compartment, with its outer rim connected oil tightly to the outer pole ring and its inner rim connected oil tightly by a staked joint to both said core and said inner pole ring in such manner as permanently to interlock and join tightly the core, the inner pole ring and the partition.

EUGENE L. SCHELLENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,933,440 Kurz Oct. 31, 1933 1,933,590 Holtz et a1 Nov. 7, 1933 2,334,040 Schellens Nov. 9, 1943 2,492,197 Schellens Dec. 27, 1949 

